In my java application i am including an image in my applet
I'm confused - is this an applet or an application? This matters because applets run under security restrictions that won't allow them to perform file I/O unless the applet is signed or the local security policy altered (you can find more about that
here).
You would use the java.awt.FileDialog or javax.swing.JFileChooser classes to browse for files.
The hardest part would be to display PPT files. I'm not aware of an AWT or Swing component that can do that. It's not hard to read PPT files with the help of the
Apache POI library, though. It lets you extract slide titles, text, images, notes and other information for each slide. You'll just have to display those in a meaningful way in the applet.